Recently, as a light source for in-vehicle headlights (driving lights, passing lights, and so on), an LED has become popular in place of a conventional tungsten-filament incandescent lamp and a discharge lamp by arc discharge. The LED can ensure required brightness with long life and less power, and further can emit light with stable brightness under a simple control that supplies a constant current thereto to be thus preferred as a light source for a vehicular lighting fixture.
Meanwhile, since the LED emits the light from a flat surface of a semiconductor chip, it has a directionality such that emission in a normal direction from the light emitting surface is intensive, but that emission in a direction parallel to the light emitting surface is very little; as a light source for the headlight that is constituted by optical members for a conventional light source that corresponds to a non-directional linear light source such as the incandescent lamp or discharge lamp, even if the LED having a light emitting part that is elongated in its optical axis direction like the conventional light source is used, the amount of light illuminating the right and left directions ahead of an vehicle is insufficient, and hence when the LED is used as the light source, the optical members for the conventional light source cannot be diverted thereto. Accordingly, for the headlight using a current LED as the light source, a newly-designed LED-dedicated optical member is generally used; however, when the above LED having the light emitting part elongated in its optical axis direction is used, and further the directionality thereof can be adapted like the conventional light source, the optical members for the conventional light source can be diverted thereto together with techniques cultivated so far, and thus compatibility with the conventional light source can be established, so that a more preferred light source for headlight can be achieved. In the following, conventional examples of the lighting fixture using the LED as the light source will be shown.
A vehicular lighting fixture according to Patent Document 1 has a configuration in which the number of LEDs to be lighted is increased in order to achieve sufficient brightness as a vehicular headlamp, in such a manner that the LEDs are arranged on the upward, downward, leftward and rightward faces of a rectangular-column base so as to arrange a large number of LEDs in a narrow space. In Patent Document 1, since the large number of LEDs that are arranged to solve the issue of the insufficiency of the amount of light are complemented in light-emission directionality with each other, there exists no problem regarding the light-emission directionality of the LED.
Accordingly, there is no description about measures to solve a problem where a light emitting element having a light-emission directionality in one direction is used alone.
Meanwhile, a vehicular headlight according to Patent Document 2 has the following configuration: while an LED with a light emitting surface elongated in a right-left direction of a vehicle is used with projector-type optical members, a concave lens is arranged between a reflection mirror and the LED in order to achieve a light distribution that is narrow in the right-left direction. In Patent Document 2, since an optical member that acts as the concave lens (typical concave lens) is provided over the front-back and right-left directions of an LED light emitting surface thereof, there exists no problem regarding the emission directionality of a rectangular-shaped LED that is elongated in an optical axis direction of the headlight (the same direction as the front-back direction of the vehicle).
Accordingly, there is no description about measures to solve a problem where a light emitting element having a light emitting surface that is almost planar and elongated in the optical axis direction is used.
Meanwhile, a vehicular headlight according to Patent Document 3 has a configuration that uses an LED with a light emitting surface elongated in the right-left direction of a vehicle, and a reflection mirror (optical member) comprising a parabolic free curved surface, in order to achieve a light distribution pattern for a low beam (passing light). In Patent Document 3, “energy distributions of a semiconductor-type light source” are disclosed in FIG. 8 and FIG. 9, and thus it is conceived that the directionality of the LED is taken into consideration. However, since the headlight is configured by a combination of the rectangular LEDs each elongated in the right-left direction of the vehicle, there exists no problem regarding the light-emission directionality of the rectangular LED elongated in the optical axis direction.
Accordingly, there is no description about measures to solve a problem where a light emitting element having a light emitting surface that is almost planar and elongated in the optical axis direction is used.
Meanwhile, an LED valve according to Patent Document 4 is configured in consideration of compatibility between a filament-type light source and an LED light source, and has a configuration in which the LED light source is mounted in a head lamp for use of the filament-type light source. On this occasion, in order to emit light equal to that from the filament-type light source to a concave reflection mirror of the head lamp, the light emitting surface of the LED is aligned in a vertical direction thereto and a reflection member is provided just in front of the LED, so that the light emitted forward from the LED is reflected by the reflection member and led to the concave reflection mirror. In Patent Document 4, the LED of which the light emitting surface is aligned in the vertical direction is used as the light source, and the light-emission directionality of the LED is adjusted by the reflection member provided just in front of the LED, but the directionality of the light emitting element that is elongated in the optical axis direction is not adjusted.
Accordingly, there is no description about measures to solve a problem where a light emitting element that is elongated in the optical axis direction is used.